The present invention relates to a stage device for use in a manufacturing apparatus or an inspection apparatus for a semiconductor device, or a microscope and/or a variety of processing machines in which fine positioning operations are carried out and also to an angle detecting device adapted to be used in a stage device and enabling a broad range of measurement while providing a high resolving power to realize a resolution of one tenth of a few second and a dynamic range of a few degrees.
A stage device is commonly employed in an apparatus for manufacturing or inspecting a semiconductor device, as well as in an apparatuses for manufacturing other precision components. In the following description, the prior art of the stage device including an associated drive mechanism and guide mechanism which is used in a apparatus for manufacturing or inspecting semiconductor devices (hereafter referred to as a substrate processing apparatus) will be explained.
In recent years, circuit integration in semiconductors, such as a LSI, continues to increase and is approaching an extremely fine line width of a pattern in a range of 0.2 μm or less. In order to manufacture or inspect such a highly integrated semiconductor, it is necessary to employ a stage device that can be highly precisely adjusted.
Such a stage device functions to retain and freely move a substrate (a wafer or a reticle) used in fabricating a semiconductor.
(1) Substrate Retaining Function:
A variety of chucking systems including a vacuum chuck, an electrostatic chuck, a mechanical chuck and the like are commonly employed for retaining a substrate; of which, an electrostatic chuck is now most commonly employed. In association with the chucking system, a variety of mechanisms are arranged for performing the following functions (2) to (5).
(2) Z-axis Directional Movement Function:
This is a function for retaining the substrate in a horizontal position on the chuck, while adjusting its height in a direction of a vertical axis (an up and down direction). This movement function is used during a focusing operation in carrying out exposure and inspection processes.
(3) Θ-axis Directional Movement Function:
This is a function for adjusting a position of the substrate held by the chuck in a direction of rotation around the vertical axis. This function is used for correcting a small angular deviation between a scanning line of a scanning axis and an array of patterns on the wafer, which will be described later.
(4) X-axis Directional Moving Function:
This is a function for moving the substrate held by the chuck in a horizontal direction. The X-axis is also referred to as a scanning axis (an axis along which a scanning movement of a movable component is performed) to expose or inspect the substrate from one end to the other end across the array of patterns thereon.
(5) Y-axis Directional Moving Function:
This is a function for moving the substrate held by the chuck in the Y-axis direction crossing at a right angle with said X-axis within a horizontal plane. In general, the Y-axis may also be referred to as a stepping axis (an axis along which a stepping movement of a movable component is performed) for stepping across the array of patterns on the substrate.
In addition to the functions described above, a further function (6) exist for use in loading or unloading the substrate onto or off the stage device. This function (6) is referred to as a “raise” function, and is employed to raise the substrate in a vertical direction upon loading or unloading the substrate onto or off the stage device, and therefore, differs from the Z-axis directional movement function designated above in (2).
The mechanisms employed to carry out the above-described functions are rigidly supported on a platen (or a platen-shaped base plate).
The substrate processing apparatus further includes a vibration isolator disposed below the base plate, which functions to prevent the transmission of vibration from a floor area to the stage device. A vibration isolator which is now in common use is designed to function so as to actively attenuate (offset) vibration during movement of a movable component of the stage device.
As will be apparent from the forgoing description, a stage device used in substrate processing apparatus is an aggregation of mechatronics and is equipped to perform a variety of functions. These functions are required to be carried out quietly and highly precisely.
Turning now to the X-axis and the Y-axis directional movement functions of the stage device, generally there are three different methods which are employed for controlling the stage device, as follow:
(a) A method which enable motion of the stage device, which comprises tables movable in any of the X-axis, the Y-axis and the Θ-axis directions to be stopped while the substrate is processed, This method is typically employed in an exposing apparatus such as a stepper for performing a step and repeat operation. By using this method, it is possible to process the substrate after vibration associated with movement of a table of the stage device has been attenuated.
(b) A method in which the X-axis (stepping axis) movable table is stopped, while the Y-axis (scanning axis) movable table is allowed to continue to move while the substrate is being processed. This method may be employed in an electron beam drawing apparatus and/or an inspection apparatus, which will be described later.
(c) A method in which both the X-axis and the Y-axis tables are allowed to move freely in carrying out substrate processing.
In the case of (a), above, any unwanted change in speed, or transmission of vibration to the stage unit, it not likely to give rise to a serious processing error. However, in the case of (b) and (c), where the substrate is moved continuously at a constant speed in an exposure or inspection operation. Any such change in speed or transmission of vibration, is likely to give rise to a serious processing error.
An essential component for controlling in a highly precise manner movement of a movable component such as a respective table of the stage device described above is a position detector. Commonly employed in a position detection method is an interference optical system. Recently, such a system has been required to be able to detect displacement of a substrate in a range of nanometers. However a problem exists with such a system in that fluctuations in interference light caused by atomspheric gas density variation in the system, which are caused by temperature fluctuations in the system, result in a deterioration in detection accuracy in the field and the field itself.
A further problem of the conventional substrate processing apparatus is that where it is required to produce a fine and highly precise pattern, as is the case in very Large Scale Integration, when a method is employed whereby light is irradiated to a photo resist film to obtain a desired patterning, an inherent restriction exists in an available wavelength of a light source employed. One method that has been proposed to solve this problem involves the use of an electron beam, instead of a light source. As technique being used in such a method there can be mentioned electron beam exposure (a charged particle beam exposure), and electron beam drawing (charged particle beam drawing). Such techniques are now being intensively developed, and involve irradiation of an electron beam into a clean space constituted of an almost complete vacuum. The same condition described above may be required for the inspection apparatus using the electron beam (or the charged particle beam).
In a substrate processing apparatus in which an electron beam is employed to detect displacement of a substrate, it is necessary to provide a stage device that is able to move the substrate in a highly precise and even manner within a vacuum. As such a unit, there currently exists one that comprises a contact type translatory guide, such as a linear motion guide (LM guide), a cross roller guide, and a sliding guide, and which are provided in combination with a drive mechanism combining a ball screw and nut with a servo motor or a supersonic motor; or in combination with a driving mechanism referred to as a friction drive mechanism, which includes a pushing shaft sandwiched between two rollers, the pushing shaft being evenly moved under driving of the rollers by means of a servo motor or a supersonic motor. Since each of the these motors is a contact-type motor, they require a lubrication oil.
Recently, an XY stage device has been employed in which a fine ceramic is utilized to form a structural member and an associated cross roller guide. This guide is used in combination with a drive mechanism comprising a direct supersonic motor to provide a translatory guide, thereby enabling a highly precise and high resolution feed operation to be effected. In a modification of such an XY stage, one in which a hydrostatic bearing is employed as a translatory guide has been suggested. Such a guide is now generally provided as a single unit, and is highly precise. However, it suffers from a drawback in that it requires an additional gas feed and/or gas exhaust piping.
It is to be noted here that in a stage device that is required to highly precisely move a substrate, if a ball screw drive mechanism is employed, it is almost impossible to eliminate deflection in a screw shaft, and therefore with each rotation of the screw shaft an undesired movement? of the ball screw is likely to occur, thereby adversely effecting positioning accuracy. Further disadvantageously, rotation of the screw shaft at high speed is likely to result in vibration and noise resulting not only (from undesirable movement) from whirling, but also from ball collision, or from collision of balls with a return tube as they circulate.
While a stage device that is directly driven by a supersonic motor may be used in a stepper for performing a step and repeat operation (that is, during an exposing operation wherein respective movable tables of the stage device are stopped), this type of stage device cannot be used in a substrate processing apparatus in which an exposure or inspection operation should be carried out with movement of respective movable tables. The reason is that excessive fluctuations in a speed of movement occur, along with vibration. Further, in an XY stage employing a hydrostatic bearing as a translatory guide, a gas feed piping and/or a gas exhaust piping prevent the stage from moving evenly.
While the demand exists for a clean substrate processing space isolated from both a space inside the substrate processing apparatus and an associated clean room environment, and containing as few gas components as possible, the contact type drive mechanism and the translatory guide mechanism according to the prior art cannot require a lubricant to operate. However, a danger exists that a lubricant may vaporize and adhere to a surface of an electronic optical system. Upon irradiation with an electron beam, the adhered vapor turns into a black-tar-like substance which is a poor conductor, thereby leading to build up of an electro-static charge in the system.
Further, there has been developed a means that a drive mechanism and translatory guide mechanism should be arranged externally to the processing space for the substrate, which provides an advantage that none of the devices used in these mechanisms is required to be specifically tailored for use in a vacuum. However, a drawback of such a means is that a space isolating or sealing mechanism is required. To this end, a magnetic fluid seal has been commonly employed in a place where a rotary shaft is introduced into a space in which a substrate is processed. However, a problem exists with this art in that a magnetic fluid utilized for the seal may vaporize and contaminate the atmosphere in which the substrate is processed. Moreover, such a seal is not sufficiently durable to effect sealing of the translatory shaft. A bellow seal commonly used to seal the translatory shaft is also problematic in that it interfere even movement of the shaft and an operating life thereof is short.
A non-contact seal is suggested in U.S. Pat. No. 4,191,385 (1980; Vacuum-Sealed Gas-Bearing Assembly). In this seal system, a moving plane is arranged to face a stationary plane with a narrow gap interposed therebetween, and plural rows of evacuation ports are formed in that plane, whereby a pressure difference can be step-wise controlled. However, such a system has not been put to practical use, although it would provide an even stage movement due to its non-contact design, since it is difficult to achieve a reliable sealing performance. The reason for this is that in this seal system, as a result of its structure a static pressure acting between each of the planes tends to vary leading to yawing and/or pitching in the stage, and thus a variation in a gap between two planes associated with movement of the stage tends to occur. A second reason resides in the fact that a displacement of a vacuum chamber, which defines the stationary plane, is measurably large in managing the sealing gap dimension.
On the other hand an encoder is commonly used as an angle-detecting device for to detecting an angle of rotation of an object such as, for example, a rotary table of Θ axis stage. The encoder comprises an optical light-emitting element and an optical photo light-accepting element each disposed in a fixed side, and a disc having a slit structure for intercepting or allowing transmission of light between them, disposed in a movable side.
For example, in an optical apparatus or the like, a rotary motor is typically employed as a device for positioning a reflective mirror with a highly precise angle, and in this case an encoder feed back control is generally employed as an angle control method, in which a rotary encoder directly coupled with the motor is used as an angle detector. In addition, a speed reduction mechanism is sometimes employed as a means for improving resolution.
However, if the encoder is used to detect the angle, an angle resolution may be restricted by an output pulse rate (pulses/rotation angle) of the encoder. Owing to this, several ideas have been taken into consideration in order to achieve a high resolution, and they include: (1) narrowing the width of each slit formed in the encoder disc mounted on a movable element side so as to increase the number of the slits; and (2) using a speed reduction mechanism for an extensive detection; and so on.
In order to realize the above-stated idea (1), such a method has been practically embodied in which a light intercepting material such as nickel is vapor deposited on a glass disc for improving the resolution. This method is based on the fact that in the prior art approach in which the slits are formed in a plate (e.g., a stainless plate) by etching, a thickness of the plate may be a factor in inhibiting the light transmission. Namely, an effective slit width in the course from a light-emitting section to a photo light-accepting section may be reduced in dependence on an inclination of the disc, wherein the narrower slit interval could bring about more serious affection and the slit could be finally blocked. From this viewpoint, the light intercepting member having a thin film may be more favorable and, therefore, a film made by a vapor deposition method as mentioned above has been employed. A method for realizing the above-stated idea (2) may cause a problem of rattling and/or back-lash from the speed reduction mechanism, which may adversely affect the precision of the device.
In this circumstance, a key to good performance is how fine and how thin a slit structure of the light-intercepting material can be formed in the encoder disc. However, as the slit width is made narrower, forming slits equally spaced circumferentially may be more difficult, which inevitably result in a condition where a diameter of the encoder disc needs to be enlarged in order to increase the resolution (because it is difficult to achieve such a detecting device having both a broad dynamic range and a fine resolution).
On the other hand, those devices having achieved good actual results in a field of measuring a linear distance and/or a linear movement include, what are referred to as, a linear encoder, a linear sensor or a laser scale. A target installed on the movable element side of such linear movement measuring means may comprise a plate (glass) having a good light transmissivity and equally spaced light intercepting materials mounted on said glass plate. Basically, this type of detecting devices has the same principle as the rotary encoder and the slit width of 0.1 μm is currently available in some detectors.
Under the conditions described above, an idea has emerged that the above-mentioned linear encoder should be applied to an angle detection of a rotating object. Starting from this idea, an influence upon a detection performance of a relative angle between a detecting device made up of a linear encoder and a target was researched, and the result presented. FIG. 30 shows a physical relationship between the detecting device and the target as well as a definition of the coordinate axes therefor. It is noted herein that a movement detecting direction is typically designated by a translatory motion axis along the X-axis direction.
First of all, the translatory motion of the target in the Z-axis direction is not detected in principle. Further, in principle, the translatory motion in the Y-axis direction is not detected. in so far as it is within a range of slit length. However, it has been found that such an event as an inclinatory motion around the Z-axis (A-axis; pitching) or an inclinatory motion around the Y-axis (B-axis; yawing) may have an influence on the detecting performance in its sensing ability and error. The reason for this arises from a factor similar to that as set forth above: “in the prior art approach in which slits are formed in a plate (e.g, a stainless plate) by etching, a thickness of the plate may be a factor in inhibiting the light transmission. That is, an effective slit width in the course from a light-emitting section to a photo light-accepting section may be reduced in dependence on an inclination of the disc, wherein the narrower slit interval could bring more serious affection and the slit could be finally blocked.” For this reason, a linear encoder could not be applied to the angle detection directly without being modified.